Reconstituted leather product and method of making



United States Patent M 3,116,290 RECGNSTITUTED LEATHER PRCDUCT AND METHGD 0F lldAKlNtG Harland H. Young, Western Springs, Edward J. Marika, Chicago, and Richard H. Eshhaugh, Hinsdale, llr, assignors to dwlfit 8: Company, Chicago, Ill., a corporation of lllinois No Drawing. Filed Jan. 8, 1957, Set. N 632,984 17 Claims. (Cl. 162-451) This invention relates to a reconstituted leather product and its method of manufacture. The product in its preferred from is a sheet of reconstituted leather fibers which has characteristics closely approximating the leather properties of color, odor, rfiexibility, surface appearance, and warmth of feel or hand.

The idea of reconstituting leather and particularly leather scraps into a usable sheet form is old and attempts have been made over the years to reduce animal leather to a pulp form and then reconstitute the fibers into a sheet resembling a hide. Various approaches have been employed, including processes which employ some of the techniques of the paper and hardboard industries. The procedures utilized in the past fall generally into five distinct classes:

Class I.l.eather, with or without other fibrous materials, is finely comminuted and handled through conventional paper or board making machinery without any added binders.

Class I1. Leather processed as in Class 1 has added to it such conventional proteinaceous binding materials as glue, casein, blood or hydrolyzed leather, and then is formed under heat and pressure into sheet or other mold ed form.

Class III.Leather fibers, alone or admixed with other fibers, are Worked into a dough form with various mastics, such as rubber, resin, rosins, oil, grease, bitumin, asphalt and the like, followed by molding into the desired shape. This technique employs organic solvents or even Water to make a semi-fluid workable mass.

Class ZV.--Leather fibers with or without other fibers, are formed into a porous felt, sometimes with the aid of paper making techniques, which felt is then dried prior to saturation with solutions or emulsions of rubber, resin, Waxes, asphalt, and other materials or" like nature.

Class V.Lea-ther fibers, with or without other fibrous extenders, are used as fibrous re-enforcement for plastic sheeting made of any of many plastic materials, e.g. polyvinyl chloride, polyvinylidene chloride, rubber, polyisobutylene, polyethylene, and other thermoplastic materials.

Defects have been present in all of the foregoing leathercontaining products, to the extent that only those products falling in Class V have become commercial realities. The unsized, or unbonded, fabrics or felts of Class I have a very low resistance to a tearing or rupturing force because of the short fiber lengths and the absence of the fiber-interlocking characteristic of natural leather. The addition of a size or binder as in Class ll does not correct these defects and, in addition, produces a stiff sheet incapable of sharp angle bends. The product of Class H also has poor resistance to tearing and resembles dried, untanned, and unplasticized hide.

The leather-containing products of Class Ill above, contain more mastic or plasticized binders than they do ddliilfifi Patented Dec. 31, 1963 fibers and since such mastics, except for bitumin and asphalt, are expensive, they have not been widely used. The more promising mastic sheets of this type have not used leather fibers at all but have made use of rags, cotton, wood, or paper pulp. High-grade, heavy-duty, asphalt roofing paper belongs in this group.

The products of Classes IV and V have been made commercially and have considerable flexibility, high strength and excellent resistance to moisture and solvents generally. They are little more than fiber reinforced plastic sheetings, however, and in addition to being expensive they possess the cold feel and the texture of plastic sheeting. Products of this type have a continuous resin film and hence are impervious and do not breathe as does leather. In the Class V product the leather fibers are used solely for the reinforcement of the plastic material and is used for flooring tiles, luggage and upholstery. However, it does not resemble leather and is not used as a substitute for leather in luxury items.

We have discovered that with suitable modifications and some additional techniques, the practices of the hardboard and paper industries, together with the use of a particular bonding resin, namely, polyvinyl acetate, and certain plasticizers, it is possible to manufacture a reconstituted leather product with properties and characteristics unattainable in the many products of the past. The raw material used in the manufacture or" our improved reconstituted leather product is mineral tanned leather, the scraps of which at the present time have little value. These leather scraps or hide pieces, if desired, properly processed may be reconstituted into sheet form of predetermined dimensions and desirable properties. The reconstituted leather sheet has many characteristic leather properties relating to color, odor, flexibility, surface appearance, and warmth of feel. The sheet, unlike most of the products of the prior art, is composed of a maximum amount of leather fibers, with a minimum of binder or resinous adhesive. The sheet is free from the characteristic resinous varnish-like, tacky, or rubbery surface commonly found in reconstituted leather products using a thermoplastic substance as the binding material. The reconstituted leather features a porosity, or moisture vapor permeability approaching that of leather, which is unattainable in products where the resin is the continuous phase of the sheet.

Attempts have been made before to convert tanned leather scrap into an aqueous fibrous pulp or stock and mat that aqueous pulp to form a sheet. The leather fibers have been invariably excessively hydrated, with the result that the ultimate sheets have proven to be objectionably brittle. Leather placed in water will take up an amount of moisture which may be called free water. A highly hydrated leather contain not only free Water, but in addition it will carry a relatively large amount of combined or bound water. Hydrated leather comprises a hydrophilic, though insoluble, protein, which tends to gelatini e when swollen b the bound water. With the practice of the method of our invention for producing a fibrous slurry, the fibers in the resulting pulp slurry are not excessively hydrated even through suspended in an aqueous medium. As pointed out above, this is highly advantageous since a reconstituted leather sheet made from excessively hydrated hide fibers is brittle. In addition, a pulp made up or highly hydrated fibers has a slow felting rate, i.e., a longer time is required to drain the water from the fibrous slurry in forming the mat, and in addition it is difficult, following felting, to express Water from a wet mat made up of hydrated pulp. This is reflected in the tendency of a highly hydrated pulp to flow or spread under pressure rather than to lose free water from the mat. In our preferred method for producing a fibrous slurry or stock from mineral tanned leather pieces, the leather pieces suspended in water are passed through a milling zone and within that zone they are subjected to a brief but intense rubbing or shearing action by closely spaced and serrated surfaces. The serrated surfaces effeet a shearing force upon the leather pieces therebetween, milling the water-carried leather pieces to a fibrous slurry or pulp. The leather is placed in a slurry or fibrous stock form in a short interval of time, requiring only a few seconds, generally under ten seconds of the intense milling is adequate. Prolonged milling of the leather is principally responsible for the hydration of the fibers and should be avoided for the best results.

We have found that only the mineral tanned leathers, e.g., chrome, alum, zirconium and iron tanned, are suitable for use in the manufacture of our improved composition. Chrome tanned scrap will normally be used because of its large volume and availability. Iron, alum and zirconium tanned leathers are not available in amounts sufficient to produce commercial quantities of scrap. There is a profound difference between mineral and bark tanned leathers. The former mills readily into well-defined fibers or fiber bundles, whereas the latter on milling yields an excessively hydrated pulp that conglomcrates into slimy, stringy masses that felt very slowly. Reasonable felting time is dependent upon the freeness of the stock and is a commercial necessity. We are of the opinion that bond is formed between the chromium or other metal ion fixed on the protein fiber and the acetate radical bonded to the polyvinyl nucleus. This bond partially explains the superiority of polyvinyl acetate as a binder for mineral tanned leather.

The lowest moisture content to which the leather has been dried in its previous handling is of significance in the preparation of the aqueous fibrous stock. The leather which has an initial or equilibrium moisture content within the range of -25% is most suitable for the preparation of stock having discrete individual fibers or fiber bundles. It has been our experience that a leather which has say a moisture content at time of milling of 50% may not be readily disintegrated to provide a stock of suitable fineness Without the danger of hydrating that leather to the point where it will take up an objectionable amount of bound or combined water. Actually this critical moisture content is the lowest moisture content to which the chrome or other mineral tanned leather has been subjected, rather than its actual moisture content at the time of milling. That is to say, a leather which has been pro-dried to amoisture level within the recom mended range of 10-25% and held there to reach an equilibrium may be placed in water prior to milling. This leather will then of course have a moisture content outside of the range, but this is not objectionable providing the leather has not been held for a period of time long enough to permit a large amount of the water to become bound, thus excessively hydrating the leather. Hence it is our recommendation that the leather used in our process have an initial moisture content within the range of 10- as such leather may be readily milled to provide the necessary fine and less hydrated fibers needed for reconstituted leather sheets having greater strength. If dried to a moisture content below 10% there is danger of embrittlement and ultimate production of shorter fibers leading to poor strength in the final sheet. If not dried to the preferred range, then coarser mill settings are required. Coarser mill settings give coarser fibers and fiber bundles which make weaker leather sheets.

' At the outset of our process we prepare a pulp or water slurry of the fibers described above. The resin, preferably With a plasticizer, is introduced into the slurry and time allowed to permit precipitation of the resin and piasticizer onto the individual fibers and fiber bundles. The slurry is then felted, draining off most of the water, to form a fibrous mat. The mat is generally cold pressed to remove more of the Water and the resulting cold pressed felt is then dried to further adjust the moisture content. Following drying the felt is hot pressed to activate the thermoplastic resin. The sheet at this point may, if desired, be subjected to further finishing.

it is essentially for the production of a good reconstituted leather sheet that the plasticizcr or plasticizers used be thoroughly mixed with the resin before addition of the resin-plasticizer mixture to the slurry. If the ma terials are not thoroughly mixed, the finished product will exhibit an unsatisfactory finish in having strained or spotty surface, and in addition the strength of the product will be impaired.

The aqueous fibrous stock must have a reasonable felt ing time in order to provide a commercially acceptable process. This may be had to some extent by raising the temperature of the fibrous stock before felting. We have discovered that the freeness of the stock may be ap-- preciably increased through the use of certain anionic surfactants added to the stool: prior to felting. The preferred class of anionic surfactant comprises sulfated fatty materials whether derived from vegetable, animal or marine sources.

It is critical that the moisture content of the mat from the felting operation be adjusted to a moisture content within the range of 10-30% before hot pressing to activate the polyvinyl acetate resin. Moisture contents in excess of 30% give an unsatisfactory bond, and moisture contents of less than 10% at the time of hot pressing result in a relatively dry board exhibiting an objectionably chalky exterior. in our preferred method the Wet felt is cold pressed at any suitable pressure remembering that excessively high pressures, rapidly applied, may cause flowing of the felt with resultant fissures or spreading. High pressures are satisfactory when gradually increased as the water is expressed. Following cold pressing the leather sheet is air dried to complete adjustment of its moisture content to within the recommended range.

it is recommended that the mat, after cold pressing and drying, be hot pressed at pressure within the range of 300-1000 p.s.i. at a temperature of -300 F. Usually a pressing time of 5 minutes is sufficient for a moderate pressure of 600 p.s.i. and a temperature of F. With the higher pressures and temperatures the time of pressing will drop accordingly and sometimes a pressing interval of as little as /2 minute will suffice. If pressures and temperatures at the lower end of the range are employed, the time should be proportionately increased. A reconstituted leather sheet may be manufactured with pressures somewhat in excess of 1000 p.s.i. but very short times of pressing would necessarily be resorted to. Pressures less than 300 p.s.i. could be employed if excessively long periods of pressure are not objectionable and generally, if such low pressures are used, it is best to increase the amounts of resin and plasticizer incorporated in the sheet.

The reconstituted leather sheet of our invention in its preferred form comprises chrome leather fibers bonded by plasticized polyvinyl acetate. The total amount of resin and plasticizer is less than the amount of leather fibers, and preferably the plasticizing composition should contain an aromatic hydrocarbon sulfonamide such as an N-substituted toluene sulfonamide. It is characteristic of our composition that the plasticized resin does not con- Stitute the continuous phase. An aromatic hydrocarbon sulfonamide, when used in conjunction with a plasticizer incorporated for low temperature flexibility, will impart a feel very similar to that of natural leather and will in addition appreciably enhance the bursting and tearing strength of the sheet. In our preferred reconstituted leather sheet the mineral tanned leather fibers make up 60 to 85% of the composition, with to 25% of the polyvinyl acetate resin, and 5 to of the plasticizing composition.

In the following discussion there are several tables or sets of data which are complete in themselves. The data of one table should not, without caution, be compared critically with that of another because of variations in testing. The Mullen test has been used as a general measure of strength and it should be remembered that the results of the Mullen test vary with temperature, humidity and thickness of the sheet. Most of the Mullen test data has been run on samples conditioned at 72 F. and 50% relative humidity. However, several of the tests have been run under other conditions which were constant for the experiments reported but not necessarily the same conditions that existed during other tests. Some differences arise because of the variation in sheet thickness from test to test. The extent of fiber reduction, the nature of the raw materials, and other variables make it necessary to generally limit comparison of results within the same experimental run. It is no coincidence that the known art and present commercial reconstituted leather products feature vegetable tanned leather scrap as the raw material in spite of the fact that chrome tanned scrap is much more abundant and available. It is our opinion that this is due to the fact that a satisfactory sheet of reconstituted mineral tanned leaher has not been previously prepared.

The properties of the leather itself are responsible for the various techniques which we use. The ease with which the leather is reduced to fiber and the type of fiber produced in pulp form is vastly different depending upon the tanning method used. Vegetable tanned leather, if dry milled, does not act too differently from chrome tanned stock. In wet milling, however, the difference is great; vegetable tanned stock produces a ropy fiber which tends to congeal into long ropy masses which are highly hydrated, whereas chrome stock produces individual fibers that tend to remain in free suspension over a wider range of conditions. Vegetable tanned stock will wet more rapidly than does chrome stock and this is probably due to its greater content of fat liquoring components. Whereas one would expect fats, resins, waxes, and other water repellants of this type to increase the moisture resistance of leather fiber the reverse is true. Therefore chrome tanned stock characterized usually by an absence of fat liquor or other lubricant does not wet readily and when reconstituted into sheet form after pulping will not rehydrate unless soaked in water for a prolonged period of time. When we use a thermoplastic resin as a binder for chrome leather fiber we then find a greater ease of hydration which is a function of the amount of resin and the amount of plasticizer. In other words the combination of resin and plasticizer which we incorporate into our reconstituted sheet functions not only as a binder but a fat liquoring agent and lubricant as well. The proper choice of resin and plasticizer is therefore critical in the control of the surface feel and other physical properties of our reconstituted sheet.

There are a number of pulp forming machines in addition to the conventional hammer or stone mills which have been used in the past in the manufacture of aqueous stock in the paper making industry. We have found that one type of machine is much more suitable than the others in the preparation of a leather fiber pulp. The type of machine which is particularly adapted to our needs is a machine which features serrated shearing surfaces with provisions for adjusting the clearance between the two surfaces. In general, then, we require a mill which has serrated plates, one shearing against the other at a predetermined clearance. We prefer to use the Bauer type mill alone or, in the case where a very fine pulp is desired, in conjunction with a Jordan mill particularly when very thin drapery stock is desired. The larger pieces of the chrome or other mineral-treated leather scrap should be first processed by a hammer mill or shredder or some other rough cutter to reduce the scrap in size so that it can be fed to the Bauer mill with some uniformity of feed. A suitable size of leather piece is that characteris tic of the industrial leather waste known as chorme shavings. There are several types of Bauer mills available and in each type of mill there is a rotation of one disc with respect to another. One type of Bauer mill has a fixed disc against which a like disc rotates. Still another type has both discs rotating in opposite directions. The leather pieces suspended in Water or with a stream of water are introduced into the milling zone defined by the two closely spaced discs at their axis of rotation and are moved outwardly with the assistance of centrifugal force to the periphery of the milling zone. During its brief passage through the mill the material is subjected to an intense shearing or rubbing force supplied by the closely spaced revolving serrated discs and by the leather rubbing against itself. This action mills the water carried leather pieces to an aqueous stock of leather fibers. The dwell time of the leather pieces in the milling zone is very brief, an average of two to ten seconds depending upon the diameter of the discs.

In the milling or grinding step water is used in order to float the stock out of the grinding zone after it has reached the desired fineness. While the amount of water used can be varied, it must be sufiicient at all times so as to force the fibers out of the mill before severe heating can take place. It has been our experience that satisfactory fiber characteristics are obtained only when the weight of the Water through the mill with the fiber is at least 4 times and preferably 10 to 20 times the dry weight of the scrap leather fed. Amounts of water less than 4 times the amount of leather results in an objectionable heating of the fibers during milling. A single passage of the material through the mill will place the leather fibers in a suitable form for subsequent processing. Multiple passages through a mill or milling through subsequent or consecutive zones may be resorted to but is not normally needed, and generally extensive milling should be avoided as it will cause an objectionable hydration and/or breaking of the fibers.

Chrome leather scraps vary greatly in their moisture content, from 60% moisture down to as low as 5%, depending upon whether the leather scrap is fresh. from the tannery or whether it has been stored a sufficiently long time so as to dry out. The lowest moisture content to Which the leather has been dried in its previous handling is a critical factor in determining the proper clearance between the shearing surfaces of the mill. We know from experience that chrome scrap leather which has been thoroughly dried, i.e., to less than 15% moisture content, will provide a satisfactory fibrous pulp upon milling in an 8" diameter disc Bauer mill where the discs are set 0.G )3"0.005 apart. Bauer mills are classified by the size of their shearing disc and are available with 8", 24", 30 and 36 discs. Obviously, the dwell time of the leather in a larger mill is somewhat greater than in a smaller mill and accordingly the clearance between the discs should be increased for the larger mills. A satisfactory leather slurry is an aqueous fibrous stock which exhibits suitable freeness and one which may be felted in reasonable time with commercial equipment. A leather scrap fresh from the tannery will generally contain from 5560% moisture and if milled with. a setting of 0.0 03"-0.Q05" in an 8 disc Bauer mill (as the dried leather scrap above) will produce a pulp that will felt so slowly as to be impractical. Therefore, stock having such high moisture content must be milled at a coarser setting, for example, 0.6250.030. If, however, the high moisture stock is predried to a moisture level of 15%, then resoaked prior to milling, it behaves as dry stock and may be 'rnilled with a setting of 0.0030.005" in an 8" disc Bauer mill. The disc clearance in either a Bauer or Jordan mill is a function of the lowest moisture content to which the chrome leather scraps have been subjected rather than to its moisture content at the time of milling. A reconstituted leather sheet composed of finely milled fibers has a greater strength than a sheet made of coarser fibers, and hence it is desirable wherever possible to use a fine mill setting.

Table I following shows a range of recommended disc clearances for different size Bauer mills for various minimum moisture levels to which the leather scrap has been subjected. This moisture content must be maintained for several hours in order to reach equilibrium conditions.

TABLE I Optimum clearances between discs for Bauer mills of various sizes (disc diameters and clearances given in inches) Minimum moisture content to which leather scrap has The freeness of a felt increases while strength decreases when the mill clearances are increased. The time required to drain the water from the fibrous slurry in the formation of the leather sheet is known as the felting time. Time for felting is a matter of choice, but obviously in a commercial operation it may not be unreasonably long and for this reason some strength will necessarily be sacificed to obtain an acceptable felting time. In some instances slower felts which produce much stronger sheets may be desirable for certain uses and if so, fe l-ting capacity must be increased in order to maintain production. The following example illustrates the relationship between mill clearances, felting time, and product strength.

Example 1 Chrome leather shavings, initially having a 50% moisturecontent, were dried in air until the moisture level reached 25%. This material suspended in water was run through an 8" Bauer mill at the several disc settings shown in Table II below and for each mill clearance one portion of the fibrous slurry was felted into a control sheet and the other portion, prior to felting, was treated with a polyvinyl acetate resin-plasticizer mix. Both the control and the resin bonded sheet were cold pressed at 300 psi. to remove free water dried to a moisture content of 20%. The sheets were hot pressed at 600 psi. for two minutes at a temperature of 140 F. The sheets were held after hot pressing for a period of time at room temperature to condition. Table 11 shows the time required for felting the control and the resin bonded sheet for each Bauer mill setting and the Mullen test data on the two completed boards. The time of felting is in seconds and is described as freeness in the table. The Mullen test data is in pounds per square inch. Freeness is the time in seconds required to pull the free water from a standard volume of the slurry at a vacuum of Hg.

Example II Chrome tanned shavings which had an initial moisture content of 12% were processed as in Example I using the various clearances indicated in Table III below between the shearing discs of an 8" Bauer mill. Samples of fibrous stocks were heated to temperatures of either 50 F. or 140 F.

TABLE III Clearances of Bauer mill shearing 0.002 0.004 0.006 0.008 0.010

Frceness of slurry of resin treated pulp felted at 50 F., sec 810 275 220 150 Mullen Test of finished sheet felted at 50 F., p.s.i 477 305 343 306 269 Freeness of slurry of resin tr pulp felted at F sec. 250 80 55 45 35 Mullen Test of finished shee felted at 140 F., p.s.i 430 370 323 320 259 Here again it is seen that freeness is poorest and strength is the greatest at close clearances of the mill discs. As these clearances increase, freeness increases and strength decreases. The data of Table ill indicates that heating the fibrous slurry prior to felting increases freeness to the point where advantage can be taken of the greater strength resulting from the closer mill settings. In the milling of chrome leather scrap containing 12% moisture, the mill settings for an 8" Bauer mill may be in a range of 0.004" to 0.008" if the pulp slurry is heated to 140 F. before felting. If the slurry is not heated then mill settings of 0.010 or greater should be used to obtain a practical felting time which will result in an accompanying decrease in strength.

Example 111 The work of this example illustrated the effect of the moisture content of the mineral tanned scrap on milling technique. Chrome shavings direct from the tannery and containing 51.1% moisture were air dried in a tumbling barrel. Samples were withdrawn after 0, 45, 90, 120, 150, 160, 180, and 200 minutes of drying time and were found to have moisture contents respectively of 55.1%, 48.5%, 44.4%, 37.2%, 30.6%, 24.8%, 14.6%. and 8% after reaching equilibrium. Each sample was passed through an 8 Bauer mill at the three disc clearances of 0.005", 0.015", and 0.025". The ratio of water to fiber through the mill in each instance was approximately 10:1. There was some little difference in dwell time among the several samples because the higher moisture stock runs through more rapidly than does lower moisture stock; however, this was not considered to be significant. Freeness (time required to form the felt from the fibrous stock) was measured as seconds required to evacuate free Water from a one foot square felt using a vacuum of 5" Hg. The dewatered felts were placed on screens, cold pressed at 300 p.s.i. and permitted to dry to equillibrium at room temperatures for two days. They were then hot pressed for 3 minutes at 140 F. and 600 psi. The finished sheets were conditioned at 50% relative humidity and 72 F., and on Weighing were found to contain 16.5% moisture. The times of felting and results of the Mullen strength tests are in Table IV.

TABLE IV Moisture Weight of Freeness in content of Clearance Frceness conditioned Mullen seconds leather of discs in seconds felts at 165% test Avg.

scrap moisture, Mullen gm. p.s.i.

Variations in the pH of the fibrous slurry at the time aldehyde. Latices of synthetic and natural rubbers are of felting has no significant effect on the strength of the board as evidenced by the Mullen test, providing excessive acidity or alkalinity is avoided. The normal pH of the slurry out of the mill is in the range of 3.5 to 5.0.

it may sometimes be desirable to mix other fibers with the leather pulp and where this is done such other fibers should be first milled according to that method which is most applicable. Other fibrous pulps can be prepared from wood, rags, linters, straw, etc, in the ways commonly used in the paper pulp industry for these materials. When incorporating non-leather fibers as extenders, simple mixing of the fiber slurries should not be resorted to. Mixing is best effected by running the combined pulps through a subsequent milling during which the discs are set relatively wide apart in order to avoid excessive fiber reduction. The addition of non-leather fibers as extenders reduces the true leather feel, warmth, flexibility, and appearance to the extent that such fibers are incorporated in the sheet.

After milling and in the instance where extenders are used, after thorough mixing of the combined fibers the fibrous stock may be used immediately or stored for future use for a reasonable length of time (few days). If storage space is limited, the milled slurry efiluent may be screened and pressed to remove excess water and stored at a consistency up to fiber solids. More concentrated slurries do not stir out well and may require remilling when diluted. Excessive milling should be avoided since it may shorten fiber lengths with corresponding reduction in strength of the final product and increase hydration of the fibers thereby making the end product more brittle.

There are a number of common resins which are unsatisfactory for our purpose, for instance urea-formaldehyde, melamine-formaldehyde, phenol-formaldehyde, and related thermo-setting resins cannot be used in the process as the major binding resin. This is probably due to the fact that they are not readily plasticized to form truly flexible binders. The same is true for the conventional proteinaceous materials such as glue, gelatin, blood, casein, peanut, and soy proteins. These latter adhesive materials are plasticized with glycerin or similar hydrophilic plasticizers which cause the finished sheet to be too susceptible to moisture and humidity even when treated with formalso unsatisfactory because they impart a typically rubbery, non-leather surface. Polyvinyl chloride, polyvinylidene chloride, nylon, polyarnides, polyethylene, and polyisobutylene resins in emulsion form are also not suitable because they do not bond the leather fibers well when introduced in the pulp slurry. These foregoing resin binders may, however, be used in small amounts as preliminary sizes or as an adjunct to the preferred polyvinyl acetate resin. Polyvinyl acetate in emulsion form is particularly suitable for the bonding of chrome and other mineral tanned leather fibers. It may be mixed or copolymerized with polyvinyl chloride, polyvinyl alcohol, polyvinylidene chloride, polyacrylic acid, polyacrylamide, polyacrylonitrile, styrene-maleic anhydride, etc., but in order to be used successfully in our process polyvinyl acetate should comprise the major portion of the total resin used as the fiber binder. It is our belief that there is a bond formed between the chromium or other metal ion carried by the tanned leather fibers and the acetate radical of the polyvinyl nucleus. The hydrophilic nature of polyvinyl acetate resin lends itself to the bonding of the hydrophilic protein fibers.

The compatibility between the chrome or other mineral tanned leather fibers and polyvinyl acetate is enhanced by use of proper amounts and types of plasticizers. There are several critical considerations in the selection of a suitable plasticizer and the formulation of plasticizer and resin used. Plasticization of the resin must be maintained at the proper level so that both resin and leather fibers receive the right proportion of plasticization or lubrication. This formulation must produce in the final sheet the strength, flexibility, and leather-like properties desired. The formulation should be such that the plasticizer or the plasticized resin does not migrate to the surface during the hot press operation thereby producing a varnished surface and hence a plastic feel to the final sheet. The formulation must provide uniform and adequate strength to the final sheet over normal atmospheric ranges of temperature and humidity. This formulation must be correlated with the humidity of the sheet at time of hot pressing and with the temperature and time at a given pressure. The formulation must be such as to avoid excessive migration of the plasticizer from the resin into the fibers themselves.

1 1 The properties of the polyvinyl acetate bound sheet may be improved through the use of certain plasticizers. We have found that the use of at least two and preferably three plasticizers is essential to the production of the preferred product. One of the plasticizers functions is primarily to render the polyvinyl acetate binder flexible over a wide range of temperatures. Either an ester type plasticizer or a substituted hydrocarbon type, or a combination thereof, may be employed for this purpose. Another plasticizer is used to impart a high bursting and tearing strength to the sheet. This latter plasticizer is of the sulfonamide type and when used in conjunction with either the ester or the substituted hydrocarbon types of plasticizer will impart a feel or hand very smilar to that of natural leather. This latter property appears only when the sulfonamide plasticizer is used with other plasticizer or plasticizers imparting low temperature flexibility. The toughness and strength provided by the sulfonamide type plasticizer is needed in the finished leather sheet even though plasticizers of the other types are used, to promote greater flexibility at lower temperatures.

The ester type plasticizer is extremely compatible with the polyvinyl acetate resin and there is little tendency for this plasticizer to migrate from the resin into the leather fiber when used at proper levels. This discourages plasticizer migration to the surface of the sheet during hot pressing. Excessive amounts of plasticizer of any type will cause oiling off which results in a staining of the final sheet. The ester type plasticizer promotes excellent .low temperature flexibility, particularly in the case of the lower alkyl phtha-lates; for example, dimethyl, diethyl, dibutyl, or mixed neutral esters such as butyl benzyl phthalate. Dibenzoyl and ditoluyl esters of the polyglycols are also particularly adaptable to imparting low temperature flexibility. All the neutral phthalate esters may be used interchangeably but it should be borne in mind that the higher alkyl ph-thalates will lubricate the leather fiber somewhat more than the lower homologues; for example, benzyl, octyl, iso-octyl, decyl phthalates are best used at lower levels, whereas ethyl, methyl and butyl esters may be incorporated at somewhat higher levels. The plasticizer formulations are selected to provide maximum flexibility at minimum cost, without appreciable sacrifice of sheet strength and toughness. The foregoing comments are applicable to all ester-type plasticizers and it should be remembered that the longer the alkyl chain of the ester, the more it functions like an oil and the greater the tendency to migrate into the leather fibers so as to produce softness at the expense of some film strength.

The substituted hydrocarbon plasticizer, like the ester type plasticizer, imparts low temperature flexibility to the leather sheet and since plasticizers of this type are generally less expensive, they may replace or at least to some extent replace, the ester-type plasticizer without too much impairment of flexibility. The substituted hydrocarbon type plasticizer is not quite as desirable as the ester type, but if used in proper proportions will provide a satisfactory reconstituted lea-ther sheet. The substituted hydrocarbon type plasticizers principal advantage is that it is more compatible with the resin than the leather fiber and consequently they do not promote water spotting or staining due to migration of the plasticizer. This type of plasticizer is also little affected by high humidities.

There are a large number of ester-type plasticizers that may be used including the neutral esters of polyb-asic acids, the oarboxylic esters of polyhydric alcohols, and the heat bodied or blown oils, the mixed alkyl, alkaryl and aryl esters of ricinoleic acid and other hydroxy monocarboxylic acids. Typical neutral esters of polybasic acids that may be used are the neutral esters of phthalic, phosphoric, adipic, azelaic, fumaric, citric, itaconic, tartaric and sebacic acids, whether the esterifying group be alkyl, aryl, alkyaryl or mixed. Another group of ester type plasticizers that may be used are the carboxylic esters of polyhydric alcohols represented by all alkyl, aryl, alkaryl, or mixed carboxylic acid esters of glycols, glycerol, pentaerythritol, polyglycols, polyglycerols, and other polyhydric materials.

The substituted hydrocarbon type plasticizer includes the halogenated hydrocarbons, such as the chlorinated paraffins and the chlorinated polyaryls. The extent of chlorination of the substituted hydrocarbons may vary and it is generally true that an increase in chlorine content enhances the strength of the sheet. The chlorinated biphenyls are particularly useful. Another substituted hydrocarbon type plasticizer adaptable to our use is the nitro polyaryls, including mono nitro polyphenyls, the mono nitro n aphthalenes and the nitro-anthracenes.

The sulfonamide type plasticizers include the aromatic hydrocarbon sulfonamides, whether or not they are N- substi uted. A particularly suitable sulfonamide type plasticizer is N-ethyl sulfonamide of mixed orthoand para toluene.

The amount of plasticizer used with respect to the polyvinyl acetate resin will depend generally upon the amount of resin binder expressed as a percent of the dry fiber and the degree of flexibility and toughness desired in the final sheet of reconstituted leather.

Inadequate mixing of the resin and plasticizer or plasticizers before addition of the mixture to the fibrous slurry will result in a weakness of the final sheet and the staining of its surface with grease spots. If the plasticizers should be added simultaneously, but not in mixture with the resin, to the fibrous stock or slurry, the finished reconstituted sheet will have a Very low strength. Maximum strengths result when the resin-plasticizer mixture is agitated for 30 minutes and is allowed to stand for one day or so before using. Five minutes agitation of the mixture improves strength somewhat, a 10 minute agitation still more; and 15 minutes gives a further increase in strength. Proper mixing is important because with the use of greater amounts of plasticizer there is a tendency for the unincorporated plasticizer to migrate to the surface of the sheet during hot pressing. Sometimes the plasticizer will carry along with it a small amount of resin and cause a spotty, varnished surface.

In the preparation of the mixture, the plasticizers being used are first rnixed together in the desired amounts until a clear compatible solution is had. It may be helpful to heat the mixture. The fluid-clear plasticizer solution is slowly poured into the aqueous resin emulsion with continuous agitation. We have found it desirable to dilute the resin emulsion (initially having a solids content of about 50%) with one part of water to 6 parts emulsion in order to compensate for the increase in viscosity which takes place when the plasticizers are incorporated. Agitation for 30 minutes is effected and the mixture is then stored for 24 hours before using. Prior to use in the slurry the plasticizer-resin mixture should be agitated. If this procedure is abbreviated, irreparable damage is done to the final product, which damage is evidenced by a softer and weaker sheet and usually a greasy, stained or spotty surface attributable to excessive migration of the plasticizer during the hot pressing operation.

The fibrous content of the aqueous leather stock to which the resin-plasticizer mix is added may be varied over a Wide range, generally from about 1% to 10%, being limited by the time required for complete precipitation of the resin and plasticizer and the difficulty of mixing heavy pulp slurries uniformly. It has been our experience that a slurry containing, say, only 0.5% leather fibers requires an excessively long time for complete precipitation and adsorption of the resin-plasticizer emulsion. If there is a milky eflluent from the felting operation that is evidence that the expensive resin-plasticizer mix has not been wholly precipitated on the fibers. Pulp slurries of 10% fiber content are difiicult to agitate, and even though the resin will precipitate rapidly it is not uniformly dispersed throughout the fiber, which will result in an inferior reconstituted leather sheet. For best results we recommend slurries containing from 1% to 6% dry fiber. Resin precipitation is normally completed in a few minutes but in case of rather dilute slurries cont-inued agitation for perhaps 15-30 minutes may be required. Normally the leather fibers will have sufficient tanning agents, chrome or other mineral tanning material, to effect complete precipitation of the resin from its emulsion, but in the event the fibers are insufiicient in tanning agents additional precipitants may be added, particularly when working with very dilute fiber slurries. Satisfactory precipitants include the syntans, bark, tannins, and the soluble salts of aluminum, iron and chromium. The normal pH of the fibers of pulp, which will be in the range of 3.5 to 5.0, is suitable for these precipitants. The pH range may be varied without impairment of the strength of the final sheet within the range of about 2.0 to 9.0. However, beyond these extremes the tanning agents have a tendency to leave the leather with resulting decrease in the freeness of the felt stock due to gelatinization.

The free water of the slurry may be separated from the leather fibers through the use of any of various available felting machines. The equipment used in the manufacture of felts for the subsequent processing into paper, hardboard, pasteboard, fibreboard, insulation board, and the like, is suitable for our purpose. Batch filters of the Chap-man Box type which involve flotation of the slurry over a flooded screen bottom, followed by evacuation under vacuum of the water through the screen, leaving a felt thereon, may be used. Continuous felting machinery such as the Oliver continuous felter is also adaptable to our processing. The Oliver felter features a rotary drum provided with an. outer screen surface and an inner mechanism for evacuation. This drum rotates partially submerged in the fibrous stock and when the felt reaches the desired thickness it is removed from the screen as a continuous felted sheet. The speed of the felting drum may be varied with the felt thickness desired.

The felt is freed of excess water by cold pressing on a screen. Cold pressing may be accomplished by hydraulic pressing with large flat surfaces or by running the felt through squeeze rolls. The pressure applied and the rate at which the pressure is applied must be correlated with felt freeness to extract water without damage to the felt. Generally speaking, when using large flat surfaces to press the board, pressures in the range of 100 to 500 p.s.i. are satisfactory. Pressures applied too quickly may cause fissures or undue spreading or flowing of the felt.

As was pointed out in the above discussion of milling of the leather pieces to form a fibrous slurry, greater strength may be imparted to the finished reconstituted leather sheet by more finely milling the fibers. However, pulp slurries containing fine fibers in contrast to more coarse fibers require longer periods of time in the felting operation to separate the free water. As mentioned earlier, heating of the slurry prior to felting is known to increase the freeness to some extent. We have found that the freeness of the slurry can be increased appreciably through use of certain anionic surfactants to the point where advantage can be taken of the greater strength resulting from closer mill settings of the Bauer mill. The anionic surfactant may be added to the fibrous slurry before or after the incorporation of the resinplasticizer mix. The one particular type of anionic surfactant which we have found to be satisfactory is sulfated fats, whether derived from vegetable, animal or marine sources. This group of anionic surfactants has a marked accelerating effect alfording a reduction of from 50 to 80% in felting time for leather fiber slurries. Cationic surfactants are unsuitable and will generally decrease freeness without appreciably increasing the strength of the finished sheets and can be generally expected to in crease felting times from to 60%. For the most part non'ionic surfactants behave like the cationic surfactants in that they increase felting time though to a lesser degree.

As will be seen from the following examples, the use of a sulfate-d fat greatly decreases felting time and effects to a limited extent a decrease in strength (for a particular mill setting) measured by Mullen test. However, the advantages to be had from an increase in the freeness of the felt Will far offset the decrease in strength due to the incorporation of the sulfated fats. Actually, from a practical manu'factuning standpoint, there will be no decrease in strength in the leather sheet produced as the use of the surfactant permits finer milling which provides a finer fiber stock and an accordingly stronger sheet. A corollary of increased freeness which is effected by the addi tion of sulfated fats is the prevention of the fibers entwining into the felting screen. Without this additive fine fibrous felts enmesh in the screen so that the felt is not easily removed without defacement, to say nothing of the expense of cleaning screens.

Example IV Chrome tanned leather scrap was dried to a moisture content of 18.1%. About 15 lbs. of the dried scrap was run through a laboratory Bauer mill with a Water ratio of 15:1 and the milling discs set at a clearance of 0.006. The milled fiber slurry was diluted with water to a solids content of 3.2%. Each test sample appearing in Table V below used 5 /2 lbs. of the fiber slurry to which a surface active agent was added prior to the addition of the resin-plasticizer mix. The resin-plasticizer mix was prepared by mixing equal parts of dibutylphthal-ate, chlorinated biphenyl (60% chlorinated), and an N-ethyl toluene sulfonamide. The foregoing mixture of the three plasticizers was poured into twice its weight of polyvinyl acetate emulsion (50% solids). The resinplastlicizer mix was mechanically agitated for 30 minutes and then aged 24 hours prior to use. 40 gm. of the resinplasticizer mix was added to each 5 /2 lbs. aliquot of slurry after the surface active agent had been mixed in.

Each felt was prepared separately by flooding a boxed screen to which a vacuum of 22 Hg was applied. The time in seconds required to pull a dry felt was a measure of freeness. This information appears in the third column of the Table V following. The felts were subsequently cold pressed, dried overnight at room temperature, and then pressed at 600 psi. and 140 F. for 3 minutes. The finished sheets were conditioned at 72 F. and 50% relative humidity prior to running the Mullen test.

TABLE V Amount Mullen basis Frccness test, lbs.

Surfactant used wt. of in per sq.

fiber, seconds in. percent Sulfated cod oil 1 190 392 Do 3 105 295 D0 a. 5 311 Sulfated castor oil 1 205 128 Do 3 150 372 0 5 1'30 350 Sultated neatsfoot O1 1 190 417 0. 3 140 35.8 D0 5 357 Sulfated red oil. 1 200 307 D0 3 140 363 Do 5 352 Sulfaterl soybean oil 1 180 374 D0 3 115 37 5 D0 5 05 261 Sullated sperm 1 215 419 0 5 105 356 None 330 476 The effectiveness of su-lfated fats is readily apparent from the table. The optimum levels appear to be about 3% sulfated oil basis dry fiber weight, since at this level there is a good improvement in freeness without too much sacrifice of Mullen test. The sulfated oils in order of increasing preference are soybean oil, red oil, neats-foot oil, sperm oil, cod oil, and castor oil.

In using sulfated oils to increase freeness the optimum level of 3% is preferred but as little as /2% basis dry fiber will prevent enmeshing of the felt fibers with the screen. Therefore, in those instances where freeness is not excessively poor but difiiculty of sticking of the felt to the screen is encountered, we would use from /2% to 1% sulfated fatty material to prevent sticking to the screen with a moderate increase in felt freeness. Excessive amounts of sulfated fatty material (7 to 10%) effectively produce the same effect, but simultaneously begin to fat liquor the stock with extreme weakening of the felt.

To manufacture the most acceptable product, the felt from the cold pressing step should be dried to a moisture content of between 10 and 30% of the total weight of the felt. This moisture content must be present at the time of hot pressing and may be achieved several ways, for example, by the use of a tunnel drier to produce a felt having a moisture content in the desired range or by excessively drying the felt and subsequently re-humidifying it to a level within the range of 10-30%.

We prefer to use a continuous drier featuring a flow of warm air countercurrent to the movement of the felt. A drier of this type minimizes case hardening and produces a felt with uniform moisture content at a level suitable for hot pressing. Case hardening of the fibers or felt may result if an excessive temperature difference and drying rate should be used. The felt should not be heated above 260 F. it has been our experience that a stream of warm air at a temperature within the range of 120 F. and 250 F. applied to the felt for /2 to 5 hours in a tunnel drier will produce a felt ready for hot pressing having :a moisture content Within the range of 12 to The felt from the cold pressing operation, if held at room temperature and at a relative humidity within the range of 20 to 90% will in time, usually in excess of 16 hours, reach a moisture content within the recommended range of 1030%. However, such long periods of time are not commercially feasible.

It is critical that the moisture content of the mat at time of hot pressing not exceed otherwise the polyvinyl acetate resin will tend to yield when the pressure is released. It is preferred that the moisture content of the board be in excess of 10% for the reason the hot pressing of a relatively dry board results in a chalky, sandy surface. The moisture content of between 10-30% seems to activate the polyvinyl acetate to give by far the best results. If the board has a moisture content much in excess of 30% there will frequently result a greasing out of the plas-ticizer to the surface of the board because of the effect of humidity or moisture on polyvinyl acetate.

During the hot pressing operation, the polyvinyl acetate resin is activated so as to provide an effective bonding of the leather fibers. Conventional systems of applying heat and pressure are satisfactory provided allowances are made for suitable control of temperature, pressure, and time at the proper level for the resin-plasticizer formulation used. Temperatures in excess of 300 F. are generally avoided because of the proteinaceous nature of the leather fibers unless time under pressure is drastically shortened. The pressing equipment can be a single or multiple opening hot plate hydraulic press as employed in the hardboard industry or it may be a series of paired rollers arranged as in the paper-making industry. In any event, the press mechanism should be capable of developing a pressure of 300 to 1000 p.s.i. for a period of time from /2 to 10 minutes (usually 5 minutes is adequate) with provisions for maintaining the temperature of the pressing surfaces from @120 to 300 F. Temperatures in excess of 300 F. are avoided because spotting or stains due to migration of the polyvinyl acetate binder and plasticizer will occur at such elevated temperatures unless the pressure is applied for a short interval. If a formula of resin and plastioizer is used which is designed to produce a softer or more flexible finished felt, it becomes necessary to decrease the temperature, pressure, and the time under pressure. The variables of time, temperature, and

T0 pressure should be integrated so as to provide a pressing cycle which will give maximum strength and most leatherlike properties at a minimum cost or equipment, labor, power and other expenses.

Obviously, if one were to use hot rolls or calender rolls typical of papermaking machinery, where exposure to temperature is very short or instantaneous, then temperatures up to 350 F. may be used. Conversely, one could press at F. for hours using very high pressures, e.g. 3000 p.s.i., and get a satisfactory sheet. However, modern production methods would generally demand the following ranges in order to minimize production costs.

Pressures 300 to 1000 lbs. per square inch. Temperatures F. to 300 F.

Times /2 min. to 10 min.

Moisture content 10% to 30%.

The following Example V demonstrates the wide variations in pressure, temperature, and time that may be selected.

Example V Chrome leather shavings with a moisture content of 22% were milled in an 8 Bauer mill set to a disc clearance of 0.015". The leather scrap was fed to the millsuspended in 20 lbs. of water for each lb. of leather. The pulp was gathered in a drum and found to contain 11.5 lbs. of dry fiber. Additional water was added to adjust the fiber solids content to 3%. 3.5 lbs. of polyvinyl acetate emulsion (50% solids) was agitated for 15 minutes while adding 1 lb. of water and a clear solution containing 0.5 lb. of dibutyl phthalate, 0.5 lb. of N-ethyl toluene sulfonamide, and 0.5 lb. of chlorinated biphenyl (60% chlorinated). When the plasticizer and the added water had been incorporated in the polyvinyl acetate emulsion, the mixture was stirred for an additional 15 minutes and the completed resin-plasticizer mixture was held for 24 hours. The following day the aged resin-plasticizer binder was added slowly to the pulp slurry at 65 F. while the slurry was vigorously agitated. Agitation was continued for 30 minutes at which time the supernatant liquor cleared, indicating complete adsorption or precipitation of the binder on the leather fiber. Solids content of the final slurry was checked and found to be 3.8%. Separate batches were weighed out and drained to form wet felts. The felts were held in a drier supplied with a stream of air at 120-140 F. for 5 hours. The dried felts were held for another 24 hours at room temperature and at the end of that period were found to have a moisture content of 18.8%. The several felts were then pressed under the conditions of time, temperature and pressure as shown in Table VI following. The Mullen tests were run after the hot pressed felts had been conditioned 16 hours at room conditions of 72 F. and 50% relative humidity.

TABLE VI Pressure in lbs. /in. Temp Time in Mullen Appearance of felt F. minutes test 3. O 340 Satisfactory.

190 0. 5 300 Slightly stained. 220 0. 25 310 Spotted.

140 4. 0 300 Satisfactory.

Spotting or stains due to migration of the binder prevail when temperatures near 200 F. are used. This is accompanied by some decrease in strength due probably to migration of the binder to the surface. This migration is also greatest at higher pressures and longer times. It can be seen also that strength increases with pressure and that the pressure and temperature are more critical than time.

The finishing of the grained surface may be achieved by any of the various techniques now used in the leather industry. Embossing by heat and pressure may be done before or after application of coloring or surface finishing. The embossing plates may be used in a flat press or as part of a pressure roller system. The moisture content of the reconstituted leather sheet should be in the same optimum range of 10-30% as recommended for hot pressing. Hence, ii the moisture content of the reconstituted leather sheet should be below 10%, it is recommended that it be rehumidified before imprinting the desired grain.

If a smooth, satin surface instead of an embossed grain is desired, the sheet may be calendered with hot rolls or smooth plate in a hot press in the fashion used for conventional leather. The preferred temperature range for finishing is in the range of ISO-200 F. and the recommended pressure range is 300-600 p.s.i. The time required for this platin operation may vary from substantially instantaneous at 180-200 F. to 30 seconds at 150- 180 F. The moisture content, like that recommended for embossing, is in the range of -30% for best results. If excessive temperatures, pressures or times are employed, the surface of the leather sheet tends to become glazed or resinous due to migration of the plasticized polyvinyl acetate resin to the surface. Migration of the resin to the surface mars the soft, leather-like finish that can be had with the use of proper temperature, pressure and time. Typical leather finishing steps such as dyeing, pigmentation, lacquering, enamelling, waxing, or polishing can be effected by the methods now in use by leather finishers. However, an advantage afforded by our method of manufacture from pulp slurries is the opportunity to produce intense colors by dyeing of the fibers in slurry form or dispersion of several pigments together in the slurry form prior to felting. Interesting mottled or marble effects can be had by mixing different colored slurries together prior to felting. The several following examples illustrate some of the various conditions and materials which may be utilized in producing a reconstituted leather sheet in accordance with the teachings of our process.

Example VI Approximately 1 lb. of chrome scrap leather was reduced in a hammermill. This scrap had a moisture content of 12%. The scrap from the hammermill was suspended in 10 lbs. of water and passed through an 8" Bauer mill set to a disc clearance of 0.006". The resulting heavy slurry was diluted with water to a consistency of 2% fiber.

24 gms. of a (50% solid) polyvinyl acetate emulsion were diluted with 4 gms. of water. The diluted emulsion was heated to 90 F. and to this was added a clear solution containing 4 gms. of dibutyl phthalate, 4 gms. of N-ethyl sulfonarnide of mixed orthoand paratoluene, and 4 gms. of a 60% chlorinated biphenyl. The polyvinyl acetate emulsion was continuously agitated while the plasticizer solution was poured slowly into it. Mixing was continued for 30 minutes and the resin-plasticizer mix was then allowed to stand for 24 hours.

The aged resin-plasticizer mix was added to 8.8 lbs. of the pulp slurry (65 F.). The slurry with the added plasticizer-resin mix was agitated for minutes at which time precipitation was completed as evidenced by a clear, non-milky, supernatant liquor.

The slurry was then poured over a screen of a felting box t id after being dispersed uniformly was evacuated to form a felt. The water was drained from the mat in approximately 3 /2 minutes. Free water was expressed by cold pressing at 300 psi. and the felt dried over night in air at 80 F. The dry felt, which had a moisture content of 16%, was hot pressed for 3 minutes at 140 F. and 600 psi. The following day the finished sheet was plated by pressing instantaneously at 180 F. and 600 psi. The final reconstituted leather sheet showed an average Mullen test of 470 lbs. per square inch.

, 178 Example VII This example was handled as in the previous example with the following variations:

Moisture content of the scrap percent 15 Disc clearance inches 0.005 Ratio of water to leather 15:1 Consistency of slurry after adjustment percent 3 Weight of slurry used lbs 5.9

Resin emulsion used: 26 gms. polyvinyl acetate (50% solids). Plasticizers used:

1 gm. butyl benzyl phthalate; 7 gms. N-ethyl toluene sulfonamide; and

4 gms. 60% chlorinated bipnenyl. Resin-plasticizer mixture aging period days 2 Time for complete resin precipitation mins 30 Temperature of felting slurry F" 70 Felting time (freeness) mins 4 Moisture in dried felt percent 17 Mullen test p.s.i 520 Example VIII This example was handled as in Example V1 with the followin variations:

Moisture content of the scrap percent 55 Clearance between discs inches 0.020 Ratio of water to leather 25:1 Consistency of slurry after adjustment percent 1 /2 Weight of slurry used lbs 11.7

Resin emulsions used:

22 gms. polyvinyl acetate (50% solids) and 2 gms. polyvinyl chloride. Plasticizers:

4 gms. dipropylene glycol dibenzoate; 4 gms. N-ethyl toluene sulfonamide; and 4 gms. O-nitro-biphenyl. Resin plasticizer mix was aged for 2 days.

Fiber slurry and binder stood overnight prior to felting.

Temperature of slurry at time of felting F 150 Felting time (freeness) min 1 /2 Temperature of drying air F .120 Drying time hrs 4 Moisture content at time of hot pressing percent" 24 Mullen test p.s.i 330 Example IX This example was run as Example V1 with the follo'v ing variations:

Alum leather shavings (55% moisture) were dried to percent 32 Clearance of discs 0.010 Ratio water to leather 20:1 Consistency of slurry after adjustment percent 3 /2 Weight of slurry for felting lbs 5.0 Resin emulsion used:

23 gms. polyvinyl acetate (50% solids);

1 gm. polyamide resin.

Plasticizers:

2 gms. butylbenzyl phthalate;

2 gms. dibutyl phthalate;

8 gms. N-ethyl toluene sulfonamide; and

2 gms. 60% chlorinated biphenyl. Aging period of resin plasticizer mix days 2 Precipitation time hr /2 Temperature of slurry at time of felting F Time of felting (freeness) min 1 /2 Temperature of drying air F 1-30 Time of drying hrs 3 /2 Moisture content of felt at time of hot press percent 20 Plating time seconds 5 Mullen test p.s.i 340 Example X This example was run'the same as Example V1 except for the following variations:

Chrome leather shavings (55% moisture) were dried to percent 24 Clearance between discs inches 0.015 Ratio of water to leather 18:1 Consistency of pulp slurry after adjustment percent" Weight of slurry used lbs 3.5

Resin emulsions used:

22 gms. polyvinyl acetate emulsion (50% solids);

24 gms. polyacrylamide solution). Plasticizers:

1 gm. dioctyl phthalate;

2 gins. dibutyl phthalate;

5 gms. N-ethyl toluene sulfonamide; and

4 gms. ortho nitro diphenyl.

Slurry plus binder stood for 1 hour before felting.

Temperature of slurry at time of ieltin F 100 Time of felting (freeness) min 2 /2 Temperature of drying air F 140 Time in drier hrs" 3 /2 Moisture content of felt at time of hot press percent 19 Temperature of press F 160 Time in press mins 2 Plating temperature F 170 Plating time sec Mullen test p.s.i 375 Example XI This example was run the same as Example VI except for the following variations:

Chrome leather shavings (55% moisture) were dried to apercent 16 Ratio of water to leather 16:1 Consistency of slurry after adjustment percent 4 Weight of slurry for felting lbs" 4.4 Resin used: 30 gms. polyvinyl acetate emulsion (50% solids).

Plasticizers used:

1 gm. diethyl phthalate;

2 gms. dibutyl phthalate;

6 grns. N-ethyl toluene sulfonamide; and

3 gms. 50% chlorinated biphenyl.

Precipitation time min 90 Temperature of slurry at time of felting F 58 Time of felting (freeness) min 3 Temperature of drying air F 150 Drying time hours 2 Moisture content of felt at time of hot press percent 22 Temperature of press F 165 Pressure in press p.s.i 300 Time in press min 2 Plating temperature F" 175 Mullen test p.s.i 440 Example X I] This example was run the same as Example VI except for the following variations:

Chrome leather shavings (55% moisture) were dried to percent 28 Clearance between discs "inch" 0.010 Ratio of Water to leather 19:1 Consistency of slurry after adjustment percent 4 Weight of slurry used lbs 4.4

Plasticizers used:

7 /2 gms. ortho nitro hiphenyl; and 7 /2 gms. I l-ethyl toluene sulfonamide.

Aging time of resin-plasticizer mix days 2 Temperature of slurry at time of felting 11- Felting time (freeness) min 1% Temperature of drier air F" Time in drier hour's 3 Moisture content of felt at time of hot press percent 25 Pressure in press p.s.i 500 Time in press min 3 /2 lating temperature F Plating time sec 30 Mullen test p.s.i 420 Example XIII This example was run the same as Example Vl except for the following variations:

Iron leather shavings (55% moisture) were dried to percent 18 Clearance between discs inch 0.008 Ratio of water to leather 20:1 Consistency of slurry after adjustment percent 3 Weight of slurry used lbs 5.9 Plasticizers used: i I

4 tglllS. ortho nitro biphei'iyl; w

4 grns. N-ethy'l toluene sulfonarnide; and

4 gms. 60% chlorinated biphenyl. Precipitation time "hours" 1 Temperature of slurry at time of felting F 60 Felting time (freeness) min 2 Temperature of drying air F 140 Drying time hrs 2 /2 Moisture content of felt at time of hot press 1 percent 21 Temperature of press rF Pressure in press p.s.i 300 Time in press min 2 Plating temperature F Mullen test 1 1 p. .i 405 The reconstituted sheet leather of our invention has many uses without surface finishing. it can be used as gasket material or as the inner crown material for metal bottle caps. These uses capitalize upon the resiliency oi the material. When finished with suitable coloring or embossing or enamelling or lacquering, all finishes used conventionally in leather working, various degrees of lustre, waterproofing, scuff resistance, and other properties can be had. The finished product has the general appearance of natural leather and is suitable for most any use Where resistance to repeated sharp flexing is not required. We do not recommend it for use as shoe uppers or soles as leather used for these purposes should have high flexibility. It is suitable, however, for inner soles and seek linings. The material is especially de sirable as decorative Wall tile or even flooring. It is excellent as a resilient underlayment for composition fl ring material or hardwood floorings. Other uses are $0 low cost clothing accessories, for example, handbags and belts, where color variety is desired and extreme wearability is not required. in the automotive industry the reconstituted leather sheet may be incorporated in door and crash panels as well as upholstery for the inside car roof and rear window shelves. This material may be laminated to a rigid structure of wood, fiber board or metal in the manufacture of luggage, providing a leather: appearance at low cost.

perforation.

various thicknesses.

board or acoustical tile, and inexpensive finished laminates for flush doors in harmony with": various decorative schemes.

In the furniture field it is use-- -ful as leather inlay vfor coffee, cocktail and card tables,. breakfront panels, and backs of television cabinets after:

Obviously many modifications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof, and there- 'fore only such limitations should be imposed as are indibated in the appended claims.

, 1. A method of manufacturing a reconstituted ileather sheet which comprises forming an aqueous fibrous stock from chrome tanned leather pieces having an initial moisture content within the range of 1025%, introducing to the aqueous fibrous stock a plasticized polyvinyl acetate resin and precipitating said resin onto the fibers of the stock, felting the aqueous stock to obtain a fibrous leather mat, adjusting the moisture content of the mat to within the range of 10-30% based on the weight of the mat, and thereafter subjecting the mat to a hot pressing operation at a temperature Within the range of 120-300 F. and at a pressure within the range of 300-1000 p.s.i.

2. A process in accordance with claim 1 wherein there is added a small amount of a sulfated fat to the aqueous stock prior to felting.

3. A process in accordance with claim 1 wherein the polyvinyl acetate resin is plasticized with a mixture of an aromatic hydrocarbon sulfonamide and a material selected from the group consisting of an ester type plasticizer and a substituted hydrocarbon type, and mixtures thereof.

4. A process in accordance with claim 1 wherein the polyvinyl acetate resin is plasticized with a mixture of an N-substituted toluene sulfonamide, a neutral ester of phthalic acid and a chlorinated aromatic hydrocarbon.

5. A method of manufacturing a reconstituted leather sheet from mineral tanned leather pieces having an initial moisture content in the range of 10-25% which comprises subjecting the leather pieces in the presence of water in a ratio of at least four parts of water to one of leather to an intense rubbing action, said leather pieces being formed into an aqueous fibrous stock within approximately ten seconds of rubbing, adding to the fibrous stock a plasticized binder containing a polyvinyl acetate emulsion as the major portion of the binder and precipitating on the fibers thereof a plasticized polyvinyl acetate resin, felting the stock to obtain a fibrous leather mat, adjusting the moisture content of the mat to within the range of 10-30%, and thereafter subjecting the mat to a hot pressing operation at a temperature Within the range of 120- 300 F. and at a pressure within the range of 300-1000 p.s.i.

6. A process in accordance with claim 5 wherein a sulfated fat is added to the aqueous stock before felting.

7. A process in accordance with claim 5 wherein the plasticizer for the binder contains as an ingredient an N-substituted toluene sulfonamide.

8. A process in accordance with claim 5 wherein the polyvinyl acetate is plasticized With a mixture of an N-substituted aromatic sulfonamide and a material selected from the group consisting of an ester type plasticizer and a substituted hydrocarbon type and mixtures thereof.

9. A method of manufacturing a reconstituted leather sheet from chrome tanned leather, said leather before processing having been dried to a moisture content of -30%, which comprises subjecting the leather in piece form and in the presence of at least four parts of water per one part of leather to an intense rubbing action, said leather pieces being placed in an aqueous fibrous stock form in less than about ten seconds of the rubbing action, introducing to the fibrous stock a plasticizer-resin mixture having at least a major portion of the resin as polyvinyl acetate, said mixture of resin and plasticizer having been sufficiently agitated prior to introduction to the stock to uniformly disperse the plasticizer throughout the resin, precipitating the plasticizer-resin mixture onto the fibers of the stock, felting the stock to provide a fibrous mat, adjusting the moisture content of the fibrous mat to within the range of 10-30%, and hot pressing the mat under a pressure of 300-1000 p.s.i. and at a temperature Within the range of 120300 F.

10. A method in accordance with claim 9 wherein the plasticizer agent is a mixture of an aromatic hydrocarbon sulfonamide and a material selected from the group consisting of an ester type plasticizer and a substituted hydrc carbon type plasticizer, and mixtures thereof.

11. A process in accordance with claim 9 wherein the plasticizing agent and resin before introduction to the stock are agitated for at least 15 minutes and wherein the plasticizing agent contains an aromatic hydrocarbon sul fonamide as an ingredient thereof.

12. A process in accordance with claim 9 wherein the plasticizing agent comprises dibutyl phthalate, N-ethyl toluene sulfonamide, and a chlorinated aromatic hydrocarbon.

13. A composition of matter comprising a predominant quantity of mineral tanned leather fibers bonded by a lesser quantity of polyvinyl acetate plasticized with an N-substituted toluene sulfonamide and as an auxiliary plasticizer chlorinated biphenyl and a neutral ester of phthalic acid.

14. A composition of matter comprising 60 to mineral tanned leather fibers, 10 to 25% polyvinyl acetate, and 5 to 15% of a plasticizing composition, said plasticizing composition being a mixture of an aromatic hydrocarbon sulfonamide and a material selected from the group consisting of an ester type plasticizer and a substituted hydrocarbon type plasticizer and mixtures thereof. 7

15. A composition of matter as depend in claim 14 wherein the N-substituted toluene sulfonamide is Nethyl toluene sulfonamide, the neutral ester of phthalic acid is dibutyl phthalate, and the halogenated hydrocarbon is a chlorinated biphenyl. V

16. A composition of matter comprising 60 to 85% chrome leather fibers, 10 to 25% polyvinyl acetate, and 5 to 15% of a plasticizing composition, which plastieiz ing composition contains substantially equal portions of an N-substituted toluene sulfonamide, a neutral ester of phthalic acid, and a halogenated hydrocarbon.

17. A reconstituted leather sheet comprising chrome leather fibers and plasticized polyvinyl acetate, in which the total amount of resin and plasticizer is less than the amount of leather fiber and wherein at least one-fourth of the total plasticizer content is an N-substituted toluene sulfonamide.

References Cited in the file of this patent UNITED STATES PATENTS 845,721 Sovereign Feb. 26, 1907 1,065,028 Clapp June 17, 1913 1,131,039 Clapp Mar. 9, 1915 1,777,831 Ferretti Oct. 7, 1930 1,795,603 Hussey Mar. 10, 1931 1,993,523 Poschel Mar. 5, 1935 2,031,629 Atkins Feb. 25, 1936 2,090,902 Runkel Aug. 24, 1937 2,158,265 Wilson May 16, 1939 2,279,771 Austin Apr. 14, 1942. 2,330,084 Scott Sept. 21, 1943 2,370,457 Gocher et a1. Feb. 27, 1945' 2,381,774 Riefenstahl Aug. 7, 1945 2,464,282 Abrahams Mar. 15, 1949 2,601,671 Wilson et al June 24, 1952 2,769,712 Wilson Nov. 6, 1956 FOREIGN PATENTS 342,908 Great Britain Feb. 12, 1931 446,893 Great Britain May 4, 1936 570,250 Great Britain June 28, 1945 594,617 Great Britain Nov. 14, 1.947

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N00 3 116 200 December 31 1963 Harland H: Young et ala It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line l3 for "from" read we form --g line 20 after "then" insert to column 2 line 60 for "through" read though --g column 3 line 35 after "that" insert a column 4 line l7 for "strained" read stained --g line l8, for "surface" read surfaces -g column 5 line 28, for "leaher" read leather column 6 line 6 for "chorme" read chrome column 13 line 10 after "bark" strike out the comma; column 22., line 32 for "depend" read defined Signed and sealed this 16th day of June 19649 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J BRENNER Attesting Officer Commissioner of Patents 

13. A COMPOSITION OF MATTER COMPRISING A PREDOMINANT QUANTITY OF MINERAL TANNED LEATHER FIBERS BONDED BY A LESSER QUANTITY OF POLYVINYL ACETATE PLASTICIZED WITH AN N-SUBSTITUTED TOLUENE SULFONAMIDE AND AS AN AUXILIARY PLASTICIZER CHLORINATED BIPHENYL AND A NEUTRAL ESTER OF PHTHALIC ACID. 